This invention constitutes an improvement over the liner configurations described in U.S. Pat. No. 3,706,203 granted to P. Goldberg and I. Segalman on Dec. 19, 1972 and U.S. Pat. No. 4,132,066 granted to G. W. Austin, Jr.; R. A. Breton; J. J. Nolan and E. E. Striebel on Jan. 2, 1979 and both of which are assigned to the assignee of this patent application. The liner as described in both of these patents exemplifies the liner construction currently being utilized, for example, in the TF-30 engine manufactured by Pratt and Whitney Aircraft Group of United Technologies Corporation, all of which are incorporated herein by reference and to which reference should be made for greater details of the construction of liners made from Finwall material. Suffice it to say that Finwall material is basically formed from either two or three pieces into panels having an inner wall and a radially spaced outer wall sandwiching either a third corrogated shell or radially depending walls defining a plurality of straight through passageways. Typically, the panels are joined at the relative ends in a louver type construction to form the liner defining the combustion chamber and the straight through passages are oriented parallel to the flow of combustion products in the combustion chamber. Because of the louver construction, each panel is radially spaced, exposing the upstream end to the cooling air coming from the compressor. Hence, the cooling air is admitted into the passageways at the upstream end and discharges at the downstream end thereof and as disclosed in the chart depicted in FIG. 4 of the 3,706,203 patent, supra, the axial temperature gradient of most of the panels vary considerably and may be as much as 500.degree.-600.degree. F. Temperature differences of this magnitude adversely affect the durability and longevity of the liner with a consequential influence on the time interval in which the liner has to be replaced.
Of significant importance the heretofore constructed liner of the type described above fabricated each panel so that the inlet of one panel was substantially in the plane of the exit of the next adjacent panel. Hence, to replace one panel, it was necessary to weld through the Finwall material, and with the state of the art welding techniques, such replacement necessitated electron beam welding.
Additionally, the heretofore known construction required that the combustion and dilution air holes pass through the Finwall material which necessitated utilizing grommets in the dilution air holes to insure continuity of upstream and downstream cooling air passageways. This not only contributed to the manufacturing complexity, but also required some means for assuring that downstream cooling air passageways did not become starved for cooling air and incur localized heating problems. For example, U.S. Pat. No. 4,132,066, supra, describes means for obviating these problems and discloses means for placing a downstream aperture in the liner wall to admit cooler air to flow counter and parallel to the combustion airflow so as to readmit cooler air on the downstream end of the grommet.
We have found that we can obviate the problems described in the above and fabricate a combustor liner utilizing Finwall material as the major portion of the liner and obtain a liner that has shown to have a higher use life than heretofore obtained as proven by actual tests with the same operating conditions of heretofore known liners. We have found that admitting the cooling air at discrete locations intermediate the ends of the Finwall panels so that a portion of air in the passageway flows counter and parallel to the combustion air, the temperature along the axial length remains substantially constant. The discharging air from adjacent panels impinge in a predescribed manner to induce a controlled film cooling effect in the space between adjacent Finwall panels also enhancing liner durability. We have found that not only does this liner panel construction reduce the axial panel temperature gradient but also reduces radial temperature gradients with a consequential reduction in the overall temperature level.
By virtue of the axially spaced Finwall panels, replacement of panels is facilitated by allowing the panel to be removed by cutting it out at the spaced intervals and inserting the new panel and with the use of a panel ring, fusion welding it in situ. This eliminates the need for the more complex and often unavailable electron beam welding which would heretofore be necessary in a multi-wall construction.
Since the dilution and combustion holes can be inserted in the spaced interval or transitional sections of the liner, the use of grommets and their attendant problems would be eliminated.